My FS gives me OPKs, and tells me to test from about day 12/13, though if you have short cycles maybe it would be worth testing from day 7? They also say use the second pee of the day afte it has been in the bladder 3 hours, as LH is usually produced in the morning, and the FMU generally isn't strong enough...

I don't know if thats standard, but thats what my FS does anyway.

Use CM as well, as OPKs don't work for everyone!